Chinese J. Chem. Eng.

, 14(4) 419—427 (2006)

REVIEWS

Advances in the Research and Development of Acrylic Acid Production from Biomass*
XU Xiaobo(许晓波), LIN Jianping(林建平) and CEN Peilin(岑沛霖)**
Institute of Bioengineering, Zhejiang University, Hangzhou 310027, China Abstract The shortage of petroleum has resulted in worldwide efforts to produce chemicals from renewable resources. Among these attempts, the possibility of producing acrylic acid from biomass has caught the eye of many researchers. Converting the carbohydrates first to lactic acid by fermentation and then dehydrating lactic acid to acrylic acid is hitherto the most effective way for producing acrylic acid from biomass. While the lactic acid fermentation has been commercialized since longer times, the dehydration process of lactic acid is still under development because of its low yield. Further efforts should be made before this process became economically feasible. Because of the existence of acrylic acid pathways in some microorganisms, strain improvement and metabolic engineering provides also a possibility to produce acrylic acid directly from biomass by fermentation. Keywords renewable resource, acrylic acid, biomass, lactic acid

INTRODUCTION Energy resources are divided into two categories: renewable and non-renewable. The fossil energy resources, such as petroleum, coal, natural gas and nuclear energy, are non-renewable, whereas solar energy, hydraulic energy, wind power as well as biomass, etc., are renewable. Nowadays, worldwide efforts to reduce atmospheric CO2 emissions and to overcome the shortage and sharp price rise of fossil energy resources, especially petroleum, simultaneously trigger research on biomass-based technologies. Renewable resources have begun to become a popular phrase. The renewable resources are inexhaustible and clean, among which, biomass is of particular importance. Biomass is the product of photosynthesis of plants and microorganisms that is produced in huge quantities every year. The majority of biomass is hydrocarbons, such as starch, semi-cellulose and cellulose, which can be hydrolyzed into fermentable sugars, mainly glucose and xylose. From fermentable sugars, various products can be produced by microbial processes, such as ethanol, organic acids, amino acids, enzymes, antibiotics, etc. Among them, ethanol and lactic acid are of special importance. Ethanol has been used as gasoline additive for many years in various countries[1] and has become the raw material for ethylene production. Traditionally, lactic acid is used in food industry, but the successful synthesis of biode-

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gradable polylactic acid opens new opportunity for lactic acid fermentation[2,3]. Compared with ethanol fermentation, lactic acid fermentation has the distinguished advantage of high productivity. When glucose is used as substrate, the theoretical and practical ethanol yields in ethanol fermentation are only 0.51 and － 0.44—0.47g·g 1 (ethanol glucose), whereas 1.0 and － 0.90—0.94g·g 1 (lactic acid glucose) can be obtained in lactic acid fermentation, respectively. Therefore, lactic acid fermentation is an atomic-saving process. Acrylic acid and its ester derivatives are principal raw materials in the manufacture of polymeric products. The polymers made of acrylic acid and its derivatives are characterized by colorless transparency, easy adhesion, elasticity, and stability to light, moderate heat as well as weathering. And they are widely applied in surface coatings, textiles, adhesives, paper treatment, polishes, leather, fibers, detergents, and super-absorbent materials, etc.[4,5]. Currently, all acrylic acid is produced from petrochemical industry by two-step gas-phase oxidation of propylene and the total worldwide productivity is more than 3 million tons per year[6]. High price of crude oil promotes the research and development of acrylic acid production from new raw materials with new technology, in which, the dehydration of lactic acid for acrylic acid production is a competitive process and has attracted many scientists and engineers to develop new proc-

Received 2005-07-19, accepted 2006-03-31. * Supported by the Special Funds for Major State Basic Research Program of China (973 Program, No.2004CCA05500). ** To whom correspondence should be addressed. E-mail: cenpl@zju.edu.cn

fermenti S. Finally.faecalis Pediococcus Leuconostoc Bifidobacterium Rhizopus oryzae Favorable carbon source glucose. alkali such as NaOH. or even hydrolytes of lignocellulosic materials[10]. Ch. lactose glucose. A wide variety of carbohydrate sources. The advantages of anaerobic fermentation include low investment and low energy consumption.or DL-lactic acid. lactose glucose. 2 LACTIC ACID FERMENTATION AND SEPARATION 2. cane or beet sugar[7]. thereby preventing the lowering of
Temperature.and hetero-lactic acid types.1 Lactic acid fermentation The commercial production of lactic acid by fermentation was started at the end of the 19th century[7]. CaCO3 and NH3 must be added to the broth to maintain a low free-lactic acid concentration in order to prevent the inhibition of bacteria. such as molasses. such as Lactobacillus delbrückii.lactis S. adsorption fermentation[17―20]. lactose glucose. The chemically synthesized lactic acid is racemic. The existing commercial production processes use homolactic organisms. maltose glucose. The fermentation technology can produce a desired stereoisomer of lactic acid or the racemate when a specific strain is used. the prospect of acrylic acid production from biomass is discussed. Then. when glucose is used as carbon source.℃ 50—53 45—55 50—60 28—32 28—32 35—40 45—55 28—32 28—32 25—32 21—25 35—45 25—35 Major products lactic acid lactic acid lactic acid LA/AA=1 1 ︰ lactic acid LA/AA/CO2=1 1︰ ︰ 1 lactic acid lactic acid lactic acid lactic acid lactic acid LA/AA=2 3 ︰ lactic acid Isomer DLDLDLDLDLDLLLDL-. 2006
. galactose glucose glucose glucose lactose glucose. Apart from treatment with alkali. August.casei L. E.9] for L-lactic acid production via hetero-lactic acid pathway. the recent advances in the research and development of lactic acid fermentation are reviewed. Reactive liquid-liquid extraction has the advantage of easy removal of lactic acid from the fermentation broth. No.leichmannii L. Lactic acid is one of the smallest chiral molecules with D-. so it is considered as one of the first biotechnological processes operated under controlled conditions. maltose glucose. L. Most of lactic acid-producing strains can be cultivated anaerobically. L. except Rhizopus oryzae[8. L. which must be cultured aerobically. the dehydration methods of lactic acid for acrylic acid production are introduced. AA—acetic acid. can be used as feedstocks. (Vol.420
Chinese J. A means to overcome the product inhibition is in situ product removal (ISPR)[11] such as extractive fermentation[12―16]. dextrose. The lactate mass concentration in the fermentation broth can reach 10%—13%. except Rhizopus oryzae. It is possible to distinguish the lactic acid fermentation as homo. L-isomers and racemic DL-lactic acid. various techniques combining fermentation process with simultaneous product separation have been proposed to continuously remove the lactic acid as it is formed. delbrückii L. Generally. the fermentation product can be D-. Microorganisms for lactic acid production and their properties are listed in Table 1. bulgaricus. However. In this article.4)
esses. 14. membrane fermentation[21―25]. their addition makes the purification process difficult and this has great environmental impact. starch hydrolytes.thermophilus L. the theoretical yield of lactic acid. LDLL-
Microorganisms for lactic acid production and their properties[7]
Note: LA—lactic acid. is 100%.thermophilus S. Reactive extraction with specified extractant giving a higher distribution coefficient has been proposed as a promising technique for the recovery of lactic acid.
Table 1 Name of strain L. sucrose glucose glucose
whey.bulgaricus L. whereas with different strains. whereas the practice yield of lactic acid is approximately 90% (by mass) in an anaerobic fermentation process. In classic industrial bioprocesses. leichmannii.

because the separation and purification steps account for up to 50% of the production costs[30]. Ch. and reverse osmosis. so high cell density is obtained.2
Figure 1
Separation and purification processes of lactic acid from fermentation broth Chinese J. The applicability of different types of organic carriers and diluents has extensively been investigated[16]. it is almost impossible to obtain pure lactic acid crystal. The lactic acid is continuously removed from the membrane as it is formed.37] have set up a whole process to
2. Secondary and tertiary long-chain alkylamines have been found to promote the extraction efficiency and selectivity. then purify lactate ester by distillation. Although the difference in boiling point between lactic acid and water is quite large. The separation and purification processes of lactic acid from fermentation broth are shown in Fig.[25] have achieved － a maximum cell density of 145g·dm 3 and a maximum － － productivity of 34g·dm 3·h 1 in cell-recycle fermentation. ion exchange resin is widely used in bioseparation and several different ion exchangers[17―20] have been used for lactate separation in the last few years.Advances in the Research and Development of Acrylic Acid Production from Biomass
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pH[13. lots of improvements have been made to reduce the high product recovery cost and the environmental impact. such as electrodialysis[21. This technique is competitive because of its high selectivity. The reasons are that lactic acid has highly affinity to water and lactate dimmer will be formed when the concentration of lactic acid is high enough.
－ －
Separation and purification of lactic acid The economics of the fermentation process depend on the development of an effective recovery method for lactic acid from broth. the amine in the solvent phase reacts with the lactic acid in the aqueous phase.14]. membrane separation.[36. such as reactive extraction. Adsorption fermentation process has been studied wherein pH value is regulated by the adsorption of lactic acid. In this method. In this bioprocesses. The lactate ester must be hydrolyzed to obtain free lactic acid and methanol. The commercial product of lactic acid is generally an aqueous solution with 85% lactic acid. extraction is carried out through precipitation stages which produce large quantities of gypsum (calcium sulfate ) that have to be treated as waste[31]. Long-chain alcohols such as 1-octanol and 1-decanol are found to be less toxic than other diluents. which results in higher productivity. Methanol and little amount of water can be removed by distillation.23]. lactic acid fermentation is investigated in a cell-recycle membrane bioreactor with a － substrate concentration as high as 120g·dm 3.. reverse osmosis membrane[22. electrodialysis.1. The calcium lactate solution is crystallized and converted into lactic acid by adding sulphuric acid. Ma et al.2g·L 1·h 1 in a fed-batch fermentation of Lactobacillus lactis[29]. Vishal Shah et al. An alternative process is to form lactic es[32―35] ter . As an efficient absorbent. In this method. Different membranes. up to 210g·L 1 L-lactic acid was obtained and the average L-lactic
acid productivity was 2.27]. resulting in the extraction of acid into the organic phase[15].24] are used in the cell-recycle. and alcohols are among the best diluents[26. such as methyl lactate. Many studies concerning lactic acid separation have been conducted using different separation techniques. But the solvents used in ISPR are toxic as they rupture the cell membrane causing the metabolite to leak out. 14(4) 419 (2006)
. According － to the work reported by Bai et al. Fed-batch process is also used in lactic acid fermentation to avoid substrate inhibition[28]. hollow fiber ultrafiltration membrane[24]. The extraction process does not affect the thermal stability of bioproducts. ion exchange. Each of these exhibits some advantages and disadvantages that are also described with fermentation processes earlier in this review. high exchange capacity and simple operation. and the energy demand is substantially low. E. chemical reaction distillation[18]. Membrane bioreactor combines the fermentation process with the simultaneous product separation. Over the past few decades.

The result indicated that decarbonylation of acetaldehyde predominated with the addition of H2SO4. and polylactic acid[45]. 2. concentration of lactate salts into free acid by bipolar membrane electrodialysis and ion exchange treatment.4 mol·L reactant solution was able to raise the pH value and increase the acrylic acid yield from 35%
Figure 2 Important chemicals produced from lactic acid[41] August. E. Acrylic acid can be produced by the catalytic dehydration of lactic acid.422
Chinese J. in addition to its traditional application in food industry.[49] conducted the experiments at 385℃and 34.4)
purify lactic acid by esterification coupling catalytic distillation.1mol·L 1 and a residence time of approximately 30s. Paparizos[48] achieved 43% acrylic acid yield at 340℃. Ch. Sawicki reported a 58% acrylic acid yield at 350℃ using Na2HPO4 on silica/alumina as catalyst with NaHCO3 as a pH adjuster. No. treated with NH3. It is promising to dehydrate lactic acid for acrylic acid production in supercritical or near-critical water. such as acetaldehyde[43]. acrylic acid. Because of their important applications in the production of biodegradable polymers and other compounds. Among these compounds. the production of acrylic acid or their ester is of special significance.40].42]. Fig. (Vol. Perry and Carl[50] reported that the addi－ tion of small amount (<0. therefore. 2006
. more acrylic acid.01mol·L 1) of Na2HPO4 to －1 the 0. it is convenient to convert lactic acid into various value-added products[41.2 shows some examples. with an initial lactic acid concentration of － 0. It includes broth clarification by cross-flow filtration[39. 14. 3 DEHYDRATION OF LACTIC ACID TO PRODUCE ACRYLATES VIA CHEMICAL REACTION There is a hydroxyl and a carboxyl group in lactic acid molecule. the catalyst was AlPO4. A completed recovery and purification process involving electromembrane operations has been reported[38]. In these processes.3-pentanedione[42]. And the most effective catalyst was the mixture of CaSO4 and Na2SO4 with the molar ratio of 25︰1.5 MPa. Holmen[46] filed a patent in
which the vapor-phase conversion of lactic acid to acrylic acid over several kinds of salt catalysts was performed for the first time. which means that after acidification. At the same time. treatment by chelating resins. In contrast. lactic acid in fermentation broth can be directly converted into acrylic acid without further processing. This novel technology has considerable prospects because of its low energy consumption and low investment. carbon dioxide and hydrogen could be produced if NaOH was added. Mok et al. lactic acid is regarded as one of the commodity or platform chemicals. propylene glycol[44]. In 1993. low-concentration lactic acid solution was used as raw material. It could give acrylic acid yield of 54% when the lactic acid solution (10%) － passed the pyrolysis tube at 10—15ml·h 1 and at [47] 400℃.

The esterification of lactic acid at the α-hydroxyl group with SA has been accomplished with 98% yield at 70℃[56]. acetoxylation can be achieved with greater than 90% yield at 73℃ and 20kPa.[57] have published their findings illustrating the whole pathways commencing from formation of 2-acetoxy propionic acid or ester by acetoxylation to production of corresponding acrylic acid or acrylate ester by pyrolysis. an effective and attractive process for conversion of lactic acid to acrylates by direct catalytic dehydration has not been realized commercially until now. Recently. The direct conversion of lactate ester or salt is favorable because the fermentation product is lactate salt and lactate ester is an intermediate during lactic acid purification. A problem with this approach was the use of expensive reagents such as acetic anhydride. these patents do not provide more information about the acrylic acid or acrylate ester product yield. first produced methyl acrylate by this process[51]. The principal competing reaction is formation of self-reaction products. The formation of esters or salts of lactic acid before conversion can ease the dehydration process. could be used to improve the leaving group capability of the α-hydroxyl group[51―54]. Michael et al. Another approach considers easily formed anhydrides. such as fermentation-derived succinic anhydride (SA). In one approach. Reacting methyl lactate with acetic anhydride at 40—60℃ gave methyl α-acetoxyl propionate with 93. The use of inert reactor packings and lesser contact times led to methyl acrylate yields of over 90% at 550℃[52―54]. acetaldehyde. which are subsequently more readily decomposed into fragments such as carbon monoxide. Using acetic acid as the azeotropic solvent. and then directly converting ester to acrylate[43]. Burns et al. such as lactide. The ester was then thermally decomposed at 500—550℃ to form methyl acrylate and acetic acid. such as acetoxylation.Advances in the Research and Development of Acrylic Acid Production from Biomass
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Figure 3
Novel approaches for “acetoxylation”
to higher than 58% molar yield on the basis of conversion (BOC) of lactic acid. Ch. The problem is the recalcitrant nature of the dehydration step although it is somewhat rectified by use of catalysts or formation of lactate. Fig. Finally. some ap-
proaches. dehydration of methyl lactate to acrylate was realized over CaSO4 catalyst in a fixed bed reactor. Paparizos[48] got 61% yield of acrylic acid from ammonium lactate. as an activating agent. and water[43]. But unfortunately.
Chinese J.5% yield. E. The highest yield was 53%.3 shows the examples. some novel methods[55―57] for activating the α-hydroxyl group to dehydration have been performed to overcome the cost factor. whereas the yield from lactic acid was just about 43%. 14(4) 419 (2006)
. The pH value was adjusted by adding ammonia during fermentation. So. Although there is a ready supply of purified lactic acid and its methyl ester. An integrated process was developed for producing lactate ester following fermentation. The preliminary replacement of the α-hydroxyl hydrogen by some other radical could avoid the lactide formation and decomposition. In recent years. Their study showed that Na2HPO4 provided moderate enhancement of the rate constant for acrylic acid production while dramatically suppressing of the rate constants for the competing decarbonylation. and then the esterification was carried out in a single step directly from ammonium lactate. inexpensive acetic acid serves as a replacement for acetic anhydride[55]. 4 POSSIBILITY OF PRODUCTION OF ACRYLIC ACID FROM LACTIC ACID BY BIOTRANSFORMATION According to the literature mentioned above. decarboxylation. For example. and secondary reactions.

and it is then dehydrated to produce acrylyl-CoA catalyzed by lactyl-CoA dehydratase. The disadvantages of the chemical processes are the requirement of high temperature and low acrylic acid productivity. The related metabolic pathway in C.4)
acrylic acid can be produced from lactic acid by chemical catalytic dehydration. can
Figure 4
Direct reduction pathway in Clostridium propionicum[62]
August. propionicum is shown in Fig. a structural analog of acrylic acid. The high price of acrylonitrile or acrylamide prohibits the commercial production of acrylic acid by these biotransformation procedures. So far. E.424
Chinese J. However. There are a few microorganisms that produce acrylic acid as an intermediate in their metabolic pathways. Although there is no clear information regarding the method to obtain a high yield of acrylic acid from renewable materials such as sugars. 2006
.[62] found the anaerobic formation of acrylic acid in the direct reduction pathway of lactic acid in Clostridium propionicum.61]. whereas the accumulation of acrylic acid is possible only when propionyl-CoA dehydrogenase is blocked. the research has
made much progress[62―65].59] and acrylamide[60. acrylic acid has been produced by bacteria from acrylonitrile[58. (Vol. The highest yield of acrylic acid was observed from acry－ lonitrile (390g·L 1). both acrylonitrile and acrylamide must be first produced from other raw materials. It is found that 3-butynoic acid ( ). Gartner et al.4. Ch. Lactyl-CoA is formed from lactic acid catalyzed by CoA-transferase. 14. No.

The conversion ratio of propionate into acrylate was about 18. Progr.2mmol·L 1 of acrylate transiently when grown on β-alanine. 323—329(1998). Amorim. Chemical Industry Press. J.L. R. 17(12). Li. 678—680(2003). Federal Republic of Germany. They co-cultured Lactobacilli and Propionibacterium shermanii to convert carbon sources into propionic acid. but the study on the dehydration of lactic acid is far from mature.M... H.E.M. which gives information regarding the feasibility of the designed fermentation process. And their final conclusion is inspiring. acrylic acid concentration never exceeded 1% of initial substrate concentration. “Study on polylactic acid fibers”. Rebitz.. in order to identify the main hurdles for the development of an industrial process for production of acrylic acid from sugars.E. (in Chinese) Hong. Römpp.. O’Brien et al.L. 5 PROSPECT OF ACRYLIC ACID PRODUCTION FROM LACTIC ACID Acrylic acid and its esters are among the most important bulk-chemicals. flavodoxin). “Lactic acid”. Basso. They discussed the toxicity of acrylic acid to potential host organisms. In both works. Y. Wang. Ind.. Biological conversion of lactic acid to produce acrylic acid is a hopeful process. Z.. 196—222(1998). 3. These reduction equivalents inhibited the further growth of microorganisms....G..J.[65] proposed another approach to produce acrylic acid. A new zeolite catalyst for lactic acid dehydration is prepared and the effectiveness is under evaluation. Except for the conversion routes mentioned above. and then. A. K. 409—417(1983). D. Fiber.[64] studied the effect of adding 3-butynoic acid on the accumulation of acrylic acid. L. a pathway for autotrophic CO2 fixation. H.. Römpp Chemie Lexikon. in a continuous fixed-bed reactor the yield of methyl acrylate by direct conversion of methyl lactate reached about 55%. Beijing.. With CaSO4 as main catalyst and reaction at 400℃. Akedo et al. From an economic point of view. Clostridium propionicum was used to further convert propionate into acrylate in the presence of an electron acceptor such as the methylene blue. (in Chinese) Yan. Synth.X.Q. Liu.[63] found that C. Recently. X. REFERENCES
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inhibit the activity of propionyl-CoA dehydrogenase. Weinheim. E. J. The technology is already mature. Lactic acid can be produced by fermentation process from renewable resources with high productivity. Biotechnol. Verlag Chemie. the researchers designed the fermentation process including acrylic acid recovery conceptually and evaluated the process economically[70]. N.5%. “Repeated-batch and continuous production of L-lactic acid by Rhizopus Chinese J. Alves. the rocketing
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